Steroid hormones, drugs, and environmental contaminants alter gene expression in target cells. For example, glucocorticoid hormones and polycyclic aromatic compounds [benzo[a]pyrene (PB), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)] induce distinct species of cytochrome P-450 in mammalian liver. The major goal of this project is to identify the molecular mechanism by which these compounds regulate expression of specific genes among the cytochrome P-450 "gene family." Glucocorticoids and polycyclic aromatic compounds bind to distinct protein "receptors" in cytosol; the ligand-receptor complexes translocate to the cell nucleus and bind to DNA. Purification of these receptors and development of anti-receptor antibodies are the specific goals of this project. During the past year, the glucocorticoid receptor has been isolated with the use of a monoclonal anti-receptor antibody. This work is directed toward rigorous structural analysis of the glucocorticoid receptor by peptide mapping and sequencing. We hope that these studies will lead directly to the use of recombinant DNA methods to clone the gene(s) for the glucocorticoid receptor. The receptor for polycyclic aromatic compounds (the Ah receptor) has been purified partially. During the past year, we have utilized somatic cell genetics to assess the function of the Ah receptor in intact cells (mouse hepatoma Hepa-1). These studies have demonstrated that nuclear uptake of the Ah receptor complex is an important step in the induction of cytochrome P1-450. The glucocorticoid receptor and the Ah receptor are analogous functionally, but alter the expression of distinct "sets" of mammalian genes. The purification of these receptors and determination of protein structure is necessary in order to understand the differential effects on gene expression.